This invention relates generally to wireless broadcast communications and, more particularly to a method of improving communications between a central control location and a plurality of remote devices.
The management of peak energy demand has long been an issue for utility companies. Load management has been extensively practiced for years with high usage, industrial and heavy commercial customers and more recently with small commercial and residential customers.
Without a central energy management system, the individual homes and businesses will generally set their thermostats at a fixed position that will assure them of a comfortable temperature in the spaces to be heated or cooled. However, it has been recognized that small changes in these temperature demands (i.e. on the order of 2 to 4°), will make very little difference to the individual user of the comfort system but will make a tremendous difference to the utility company during periods of high demand. That is, during periods of unusually high electric demand, the power company can send out a wireless broadcast signal to its user thermostats to adjust (i.e. set-back) the thermostat temperatures by a few degrees from the standard setting and then return it to the existing setting when the power emergency is over. In this way, the homeowner will be slightly inconvenienced, but the resulting reduction in energy usage could eliminate price spikes and help curb blackouts and brownouts.
The communication that is necessary between the utility company and the energy users is critical for the purposes of 1) ensuring that the set-back signals are received by the users and 2) to inform the utility if and when the set-back condition has occurred. One approach is that of sending individual messages to each and every device. While effective, this approach is much too time consuming, both in the sending of the set-back messages to the user and in receiving acknowledgment from the user.
Another approach is that of having each of the user devices being programmed to listen to a particular wireless broadcast channel assigned for that utility, and then broadcasting the set-back messages by way of a single transmission. The problem with broadcast messages is that, unlike an individual message addressed to a particular device, the broadcast message is simply sent out without any acknowledgment of receipt or any mechanism for retry. This makes the broadcast message less effective then the individual message because not all of the devices will “hear” the broadcast message even though they may be able to “hear” the individual message.
While it is possible to broadcast a set-back message and have the individual users acknowledge receipt by way of their two way communication capability, the ability to handle those acknowledgment responses is proportionately limited by the total number of installed devices. That is, since there is no way to simultaneously receive and record all of the various acknowledgment responses instantly, it is necessary to spread out or stagger those responses over a period of time proportionate to the number of installed devices in order for them to be received and recorded. This is due to bandwidth limitations of the underlying wireless communications (i.e. the number of simultaneous messages that can be handled by a transceiver). For example, with a user base numbering in the range of twenty-five thousand, the responses must necessarily be spread out over a period of two hours. While this substantially hinders the utility's ability to monitor the responses, the overall effectiveness of the broadcast message (i.e. the actual number of installed devices that “hear” the message) is the most critical measure of success for the utility. The larger the number of devices that “hear” the broadcast set-back message, the greater the reduction in energy demand.